I used that route frequently in the early 1970s, travelling from my parent's home in Ipswich to Sheffield (with no changing required). It had some of the oldest rolling stock in the country, with the 'corridor + compartment' coaches where clouds of dust rose from the seats when you sat down. There was always a buffet car on the train but there was rarely anyone to actually staff it!
As has been mentioned above, the service disappeared when the railways were privatised (presumably because no single operator could make it pay).
You can, with several changes of train, still travel along the same route (Parkeston Quay [now Harwich International], Ipswich, Stowmarket, Bury St Edmunds, Ely, March, Peterborough, Sheffield Midland [now simply Sheffield], Manchester Piccadilly and Liverpool).
However, to connect to or from the daily StenaLine ferries, there's now a daily through train from Harwich International to Cambridge, which might provide more convenient connections for some travellers.
Chris